Recently, responding to the increasing demand for automated paper handling systems for copying machines, optional systems such as an automatic document feeding system and a sorting system designed for sorting or grouping copied sheets have been developed and commercialized in various types. The users of the copying machines are now requiring a sorter-finisher capable of automatically binding and stacking sheets which have been distributed in the sorting system, and this type of sorter-finisher has already been commercialized for some of large-sized copying machines. Also, a compact sorter having a plurality of bins disposed one upon another, wherein the bins are moved in order from the top bin to the bottom to enlarge the space between the bins so that sheets are distributed among the bins, has been commercialized.
If a sheet binding function is provided for this type of sorter having movable bins, the bins should be moved to a sheet take-out position where sheets are transported into a binding unit orderly from the bottom bin to the top. However, since sheets are distributed into the bins in order from the top, in a stapling process, the bins are moved one by one to the take-out position orderly from the bottom bin which have no sheets therein Accordingly, This type of sorter-finisher has a problem of loss of time.
Also, in using this type of sorter-finisher, when an operator notices the necessity of a stapling process in the middle of a copying operation without selecting a finishing mode in the first place in which a stapling process is executed, the operator should cancel the current copying operation and thereafter select a copying mode again to start another copying operation. This is troublesome and not economical.